Sorry, there isn’t. For details of more Garmin weirdness see here: http://www.gwprojects.org/forum/viewtopic.php?p=26674#p26674
If you use this POI code then it will show up in the GPSr in searches for fuel!
Garmin won’t tell us, of course, but since it shows up in searches for both gas and shopping I think this type should only be applied to gas stations with an attached shop. Don’t use this for convenience stores without fuel pumps.